Vol 90, No 8 (2019)

Abstract—Electromagnetic overcurrent releases have become widespread among electromagnetic devices in control systems and electrical energy distribution when protecting against negative effects of short-circuit currents. They should provide a high speed when the electrical circuit us broken in the emergency mode. This can be achieved with a small mass of a moving element and significant values of electromagnetic force. For the purpose of approximate determination of the characteristics, the methods of the theory of circuits are still widely used. By simplifying the structure of the magnetic field model, the conductivity of air gaps between ferromagnetic elements of the magnetic system can be determined with reasonable accuracy using a modified probable magnetic flux path method.

Abstract—One effective overvoltage control method for the automatic reclosing cycle (ARC) of long-distance high-voltage transmission lines is intelligent automatic reclosing. The method is based on the selection of a reclosing time that is optimal for reducing the intensity of the transient process. The article investigates the basic transient process patterns in the ARC and analyzes various automatic reclosing methods. The principle of superposition is used for the analysis as well as the proposed universal electrical network model, which describes the processes at all ARC stages. It is shown that the intensity of the transient process at the automatic reclosing directly depends on the ratio of the supply voltage and line voltage at the reclosing time. It is shown that the overvoltage level can be reduced by line reclosing at the breaker contacts’ voltage zero-crossing time or at the valley point of this voltage envelope, but the intelligent automatic reclosing is more effective, combining both approaches and performing reclosing at the zero-crossing time near the envelope valley. Computational experiments confirm that the reclosing time has a decisive influence on the overvoltage in the ARC, while the influence of the compensation degree and transmission angle is not so important.

Abstract—The approximate expressions for calculating currents at an inverter’s output and at the input of the output rectifier, as well as the efficiency and load characteristics of a dc–dc converter, are obtained on the basis of a linear equivalent circuit of a dc–dc converter under the assumption that the current is sinusoidal at the inverter’s output. A fundamental harmonic method is used for this purpose. We compare characteristics of a dc–dc converter obtained theoretically by taking into account and not taking into account the active resistance of the LC circuit and also with characteristics obtained using the Simulink model. It is shown that calculations performed with the help of the fundamental harmonic method are in good agreement with real parameters of a dc–dc converter of LCL-T type. The obtained relationships make it possible to identify features of the dc–dc converter, and, if we compare the results with the results of imitation simulation, we will be able to determine possible errors of the method caused mainly by nonsinusoidal current consumed from the inverter bridge.

Abstract—The scientific and methodological principles of development of the design models of a new device—station service voltage transformers intended for use in design study—are considered. The proposed models relate to the “white box” model class, which provide the maximum accuracy when solving such problems. The models are based on equivalent circuits of active parts, which are obtained using the principle of duality of magnetic and electric circuits. It is revealed that the determination of parameters and verification of models are possible only at the manufacturing plant of transformers. Special attention is paid to reproduction in the models of magnetizing process of transformer. The experimental oscillograms are given of magnetizing currents of magnetic conductors of the active parts and of the transformers as an assembly, which show the capacitances of high-voltage winding have a great effect on the open-circuit current. The algorithm for determination of the parameters of transformer model for calculation of steady state conditions is presented, which provides a good coincidence with experimental values for integral parameters, such as the power loss and the root-mean-square value of magnetizing current.

Abstract—When designing a transformer structure and numerical simulation, it is needed to calculate the parameters of an equivalent circuit. One of the most important parameters is the leakage inductance of two windings or of their parts, the calculation of which can be relatively easily performed solely for simple cases of equal high windings. For more complex configurations, it is necessary to apply special methods, which are developed mainly for calculating the leakage inductances of high-power network transformers. Among these methods, one can distinguish the method of average geometric distances, methods based on the analytical solution of Maxwell’s equations in a two-dimensional axisymmetric statement, and the numerical finite elements method. In this work, these methods are used to calculate the leakage inductances of small-sized transformers with winding configurations typical for voltage transformers of inductive type and station service voltage transformers. The accuracy of methods is estimated by comparing the calculation results with experiment. The description of the experimental setup is presented, the general characteristics of calculation methods are given, and the results of comparison of calculated and experimental values of leakage inductances are analyzed.

Abstract—Two units of an RZhFA-6500 reactor were put into operation into a current return circuit of the Uglerod traction substation of the West Siberian Railroad in series connection with RBFA-U-6500/3250 reactor as a part of a resonant-aperiodic L-shaped filter device. Before assembling the new type reactor, its inductances were measured with the ammeter–voltmeter method under alternating current. The phase-shift angle between current and voltage drop on the RZhFA-6500 reactor was not controlled. To check the operability of the new of type reactor and analyze its efficiency, a series of experiments in the regular and emergency operation modes of the dc traction power supply system were conducted. An experiment using a forced short circuit without cessation of the motion of electric vehicle over the section was performed. Oscillograms at the catenary feeder and the circuit of traction current return were synchronously recorded upon disconnection of a high-speed switch. A comparative analysis of harmonic composition of the voltage drops on the reactors of two types was carried out. The amplitude–frequency responses of traction current for different operation modes of the Uglerod traction substation were plotted. The method for calculation of the RZhFA-6500 reactor inductance based on recorded oscillograms in regular and emergency operation modes of the traction power supply system was developed and tested. A universal formula for inductance calculation taking into account the phase-shift angle between the current and the voltage drop on the reactor when measurements by the ammeter–voltmeter method was derived.